1. Field of the Invention
The present invention relates to a recording tape cartridge having a case body formed by a top case half and a bottom case half for accommodating a recording tape with a lid fitting manner, wherein the case body is arranged to improve the mechanical strength of the cartridge.
2. Description of the Prior Art
In a recording tape cartridge of the type mentioned above, the feed precision of the recording tape depends largely on the flatness of and the parallelity between the top and bottom case halves when the case halves are assembled. The assembling precision as well as the molding precision of the top and bottom case halves have a strong influence upon the improvement of the feed precision of the recording tape. Moreover, the mechanical strength of the case body upon completion should be improved in order to prevent a deformation thereof when it is subjected to an external force and to a high temperature environment. Particularly in case of a recording tape cartridge in which the recording tape is fed in the manner of reel-to-reel, that is, the recording tape is released from one tape reel to the front of the case body and taken up on another tape reel, the mechanical strength of the case body should be sufficiently strong to ensure against deformation because of the ease in which as case body becomes deformed in the horizontal longitudinal direction when used in a reel-to-reel manner.
Conventionally there have been proposed various techniques for preventing deformation of a case body as mentioned below.
First, Japanese Utility Model Publication (unexamined) No. 48478/1986 and Japanese Utility Model Publication (unexamined) No. 145783/1984 disclose to engage the screw bosses of the top and bottom case halves to the respective receiving means, in addition to engaging the halves by means of joining a cut recess and a projection formed on the butting surfaces of surrounding walls of the top and bottom case halves so as to prevent slipping between the top case half and bottom case half on the surrounding butting portion.
Second, Japanese Utility Model Publication (unexamined) No. 145782/1984 discloses that in order to prevent the slipping between the top and bottom case halves on the butting portion, there are formed projection members for preventing the shift of the butting surfaces of the top and bottom case halves caused by the deformation inside the butting surfaces of the top and bottom case halves whereby the resilient deformation can be reduced.
Further, there is an example of the recording tape cartridge such as disclosed in laid opened in Japanese Utility Model Publication No. 38194/1977, in which a high feed precision of the recording tape is required. In the above-mentioned recording tape cartridge a number of tracks are provided on the recording tape so that the width of the respective tracks is extremely narrow. Moreover, in the case of a tape dubbing operation, since the recording tape feed speed is set extremely high, the recording signal tends to drop out if the feed precision of the recording tape is low.
In the above-mentioned recording tape cartridge, the tape feed direction for recording is limited to one direction and there is defined an opening near the central portion in a rear peripheral wall of the cartridge case for discriminating the tape feed direction. Therefore, such an opening causes the cartridge case to be more easily deformed easier in the vertical direction as compared with a case body which does not have this opening.
In the case of a recording tape cartridge such as an audio tape cartridge of the Philips type or a digital audio tape cartridge, the interval between the screw bosses for fastening the top and bottom case halves in the rear peripheral portion of the case body is large and the butting member of the top and bottom case halves at the rear portion of the case body is limited to the rear peripheral wall of the case body, therefore, the case body is more easily deformed in the vertical direction or in the horizontal direction as compared with the video tape cartridge.
As described above, in the recording tape cartridge in which the deformation of the case body is prevented by the mechanical engagement structure such as the recess and projection formed on the peripheral walls of the top and bottom case halves for preventing the slipping movement of both the top and bottom case halves, the cartridge case can show an effective mechanical strength against only one deforming. In other words, there occurs a directionality in the effect of preventinmg deformation. For example, in the case of the recording tape cartridge with the groove and projection engagement on the butting surface of the rear peripheral walls of the top and bottom case halves (disclosed in the above-mentioned Japanese Utility Model Publication No. 145783/1084), the cartridge case has an effective mechanical strength against the deformation force applied in the vertical direction to the rear peripheral walls of the top and bottom case halves but has no effect on the external force such as a forth which causes the rear peripheral walls of the top and bottom case halves to slip back and forth.
As described above, there have been at once strength and weaknesses in the conventionmal techniques for preventing deformation of the tape cartridge case. Therefore, it has been difficult to sufficiently ensure the mechanical strength of the cartridge case and there has been a limit in the degree of improvement of the feed precision of the recording tape.